|Publication number||US7249769 B2|
|Application number||US 11/166,727|
|Publication date||Jul 31, 2007|
|Filing date||Jun 27, 2005|
|Priority date||Nov 22, 2000|
|Also published as||DE60116455D1, DE60116455T2, EP1209389A2, EP1209389A3, EP1209389B1, US20020060432, US20050285345|
|Publication number||11166727, 166727, US 7249769 B2, US 7249769B2, US-B2-7249769, US7249769 B2, US7249769B2|
|Inventors||John R Webster|
|Original Assignee||Rolls-Royce Plc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (16), Classifications (13), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to seal apparatus. More specifically but not exclusively this invention relates to a seal for sealing between one rotating member and one static member.
It is frequently necessary to seal a clearance gap between two components that are capable of relative movement. In particular one or more seals are often required to provide a seal between a rotatable shaft and an axially adjacent static component. For example, a gas turbine engine comprises shafts which rotate at relatively high speeds and which are exposed to pressurised hot gases. Seals are required between rotating rotor blades and surrounding static casing structure.
Seals are also required between a rotor carrying such rotor blades and an adjacent static structure which carries stator vanes or nozzle guide vanes. In a gas turbine engine nozzle guide vanes or stator vanes are non-rotating and as such mounted on a static structure.
It is also important to provide such seals to prevent hot pressurised gas in one pressure zone flowing freely into an adjacent lower pressure zone.
It is well known to provide labyrinth seals to seal between rotating and non-rotating members, however large clearances are required at some engine operating conditions to accommodate relative movement. It is desirable to reduce or alter these clearances at certain operating conditions to achieve the most effective power output of the engine.
It is also a requirement of such seals that an acceptable clearance gap is provided at all the differing engine conditions. Such seals between rotating and non-rotating members are not required to provide a complete closed seal but are required to provide a seal with a predetermined clearance range.
Thermal expansion and changes in pressure conditions can also cause unbalanced forces on the seal and affect the seals effectiveness. It is therefore important that the clearance between the non-rotating part of the seal and its static part is kept within a predetermined range.
It is therefore an aim of the present invention to provide an improved seal which may also alleviate the aforementioned problems.
According to the present invention there is provided a seal for providing sealing between at least two separate and differing pressure zones and between a rotating structure and non-rotating structures, comprising first and second sealing means, the first sealing means comprising first and second seal lands positioned either side of a rotating seal member, said seal lands being connected together via connecting means, said connecting means being movably mounted on said non-rotating structure and arranged to be moveable so as to accommodate relative movement of said rotating and non-rotating structures, said second seal member being arranged and positioned to provide a seal between said non-rotating structure and the first seal land positioned in a lower pressure zone such that the pressure around this seal land is controlled.
The seal lands may comprise two opposing magnets arranged to repel one another.
Preferably the sealing lands comprise rings.
Also preferably the sealing member comprises a rotating sealing fin attached to a rotor of a gas turbine engine.
The connecting means may comprise a yoke.
The yoke may be connected to the non-rotating member by a first pivot, allowing rotational movement of the yoke.
The opposing faces of the seal lands may comprise reduced area portion positioned opposite one another.
A gas turbine engine 10 is shown in
The gas turbine engine 10 operates conventionally in that air is compressed as it flows through the fan section 14, the intermediate pressure compressor section 16 and the high pressure compressor section 18. The air is then delivered into the combustion section 20 and fuel is injected into the combustion section 20 and burnt in the air to produce hot gases. These hot gases flow through and drive the high pressure turbine section 22, the intermediate pressure turbine section 24 and the low pressure turbine section 26. The hot gases then flow through the outlet 28 to provide some thrust. However, the main thrust is provided by the air compressed by the fan section 14 and discharged through the fan outlet 30.
A seal arrangement 40 is described below with respect to a gas turbine engine, although it is to be appreciated that the seal is suitable for any application between relatively moveable components where sealing is required.
A number of pressure zones or chambers are located around sealing apparatus 40, which could be considered to be the high pressure and low pressure zones or chambers located within the compressor or turbine of a gas turbine engine. One side of the rotating fin 46 and attached structure is adjacent a high pressure zone or first chamber 60. The other side of the rotating member 42 and its attached sealing fin 46 is adjacent a low pressure zone or second chamber 62.
The relative position between the sealing fin 46 and the static structure 52 is altered during normal operation due to factors such as differential thermal expansion, centrifugal growth, and changes in pressure. The purpose of the seal is to prevent passage of fluid from the high pressure zone 60 to the low pressure zone 62. Forces are generated in the moveable segment by pressures around the elements and any bias which may be applied by the leaf. springs 56.
As the forces produced by pressure changes increase, the magnetic restoring forces need to increase to accommodate such changes. If such forces generated by pressure differences on the seal 40 are reduced then the seal 40 can be more responsive and less expensive.
A second seal 64 is therefore located such that a seal between the high pressure zone 60 and low pressure zone 62 is not only provided by sealing fin 46 but also secondary seal 64. In this conceptual example of the present invention a secondary seal 64 comprises a second sealing fin 66 located outwardly from magnetic ring 50, this fin 66 would also be formed as a disc. The fin 46 is in sealing contact with secondary seal 68 which is attached to casing 52.
The main function of first sealing fin 46 is to maintain a suitable clearance gap thus accommodating displacement of the static member 52 or rotating member 42 in response to pressure changes and in general to any movement between said static member 52 and rotating member 42.
Pressure distribution around the seal may be controlled by effective positioning of the secondary seal 64. Without such a secondary seal 64 the main seal 40 is required to provide magnetic forces to counter large forces provided by pressure differences. The positioning of the secondary seal 64 as shown in
Full pressure balancing may be obtained by arranging or positioning the secondary seal such that an area equal to half of the main seal land area is subject to the high pressure. The main seal land area is indicated by small letter ‘a’ and the secondary seal land area is indicated by small letter ‘f’.
This concept can be understood more clearly by referring to
The force, F, on magnet 48 is derived as follows:
The forces on face a, Fa are defined by
HP is high pressure and a is area of face a
The force on face b, Fb is defined by Fb=HPb, where b is the area of face b
The force on face c, Fc is defined by Fc=½(HP+IP)c, where c is the area of face c and IP is an pressure intermediate high pressure and low pressure, this is a simplifying assumption that the pressure IP is midway between pressure HP and pressure IP,
The force on face b is balanced by the force on equivalent part of a and so for this calculation may be disregarded.
The term ½ (HP+IP) is used to give the average pressure over area c. This is an approximation only, but provides a reasonably good first order approximation. The force to the right on magnet 48 is therefore:
F 1 =HPc−½(HP+IP)c
Similarly the force, F2, on magnet 50 is
The force on face e is balanced by the force on face g and may be disregarded.
F 2=½(IP+LP)d−f HP−(d−f)LP (assuming f<d), c=d
if a value of f=d/2 is used, then F1+F2=0
i.e. the forces F1 and F2 are completely balanced.
Some forces will be generated by flow effects (Bernoulli etc.) and by imperfections in the balancing. Forces will also be needed to accelerate movement of the magnets and associated mechanism during rapid transients.
The area of pressure lands of the magnets 48 and 50 are reduced, as indicated by c and d and may be used to reduce the effect or imperfections by allowing the forces to act only on smaller areas. The seal still operates without the reduced land i.e. c=a, b=o, but higher forces may be generated, leading to the need for higher magnetic forces, size, weight, etc. The same principle may be used with other force generating mechanisms.
Thus it can be appreciated that changes in pressures as the yoke 54 moves axially, will produce forces which restore it to a position where equal gaps are achieved on either side of the sealing fin 46 thus providing a fully pressure balanced seal.
A practical application of the concept indicated in
A secondary seal 84 is provided, and this secondary seal 84 comprises a hook type protrusion 86 on said stator structure 73 and a co-operating seal land 88 mounted on said yoke 78.
The positioning of this secondary seal 84 prevents low pressure air indicated in
The secondary seal 84 is positioned to follow an arc around the pivot point 80. This position of the secondary seal 84 is chosen to balance the rotational forces generated by the pressures around the pivot point 80. Using the pressure balance equation previously noted in this specification, it is clear that pressure balance can be obtained by arranging the secondary seal 84 to be provided with a seal land area calculated for pressure balancing.
Conventionally in magnetic levitating seals or air riding seals etc. a gap closing force is applied which is opposed by levitation. This requires large forces to be generated or maintained to overcome this closing force. The present invention reduces this closing force which allows the seal to be smaller, lighter and be provided by a lower cost structure. Such a seal arrangement also provides a possibility for a faster response to movements of the sealing structures. The present invention arranges two seals to operate in opposition with any pressure forces being totally or partially balanced.
Another embodiment of the present invention is shown in
An alternative embodiment of the present invention is shown in
A further embodiment of the present invention is shown in
An additional embodiment of the present invention is shown in
A further embodiment of the present invention is shown in
In operation fluid flows from the high pressure zone 60, to the low pressure zone 62 through the seal 150. The fluid initially flows in the direction of arrows A along the surface 46A of the sealing fin 46 towards the tip 47 of the sealing fin 46. The fluid is directed to flow away from the surface 46A by the curved surface portion 47A of the tip 47 towards the magnet 48. Additionally the curved surface portion 47C of the tip 47 directs the fluid away from the surface portion 47B towards the yoke portion 54A. This directing of fluid flow towards the magnet 48 increases the lift between the sealing fin 46 and the magnet 48 and yoke 54. Similarly the fluid flows in the direction of arrows B along the surface 47H of the tip 47 of the sealing fin 46 towards the surface 46B of the sealing fin 46. The fluid is directed to flow away from the surface 47H by the curved surface portion 47G of the tip 47 towards the magnet 50. Additionally the curved surface portion 47E of the tip 47 directs the fluid away from the surface portion 47F towards the yoke portion 54B. This directing of fluid towards the magnet 50 increases the lift between the sealing fin 46 and the magnet 50/yoke 54. This is because the fluid velocity in a small clearance gap is greater than the fluid velocity in a large clearance gap for the same mass flow and hence there is a greater force with a small clearance gap. The clearance gap is of the order of 80 μm in width and 10 mm long.
Although the present invention has described a stepped sealing fin for the magnetic seal it is equally possible to apply the principle to an air riding seal, brush seal and labyrinth seal.
Although the present invention has described the use of spring, or pivot, mounting of the connection between the seal lands to the static structure other suitable methods may be used.
Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.
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|U.S. Classification||277/411, 277/410, 277/421, 277/412|
|International Classification||F01D11/02, F16J15/32, F16J15/447|
|Cooperative Classification||F16J15/3288, F01D11/025, F16J15/4472|
|European Classification||F16J15/447B, F16J15/32G2, F01D11/02B|
|Jan 26, 2011||FPAY||Fee payment|
Year of fee payment: 4
|Feb 2, 2015||FPAY||Fee payment|
Year of fee payment: 8